1. Field of the Invention
The present invention relates to a terminal modifier for conjugated diene polymers. More particularly, the present invention relates to a terminal modifier having both at least two amine groups and at least one alkoxysilane group, a terminally modified conjugated diene polymer which is coupled at the terminus with the terminal modifier, and a polymer composition for use in tires, comprising the terminally modified, conjugated diene polymer.
2. Description of the Related Art
Recently, with the growing concern with environment-friendly, energy-saving high-performance tires, extensive research has been directed toward high functionality rubber. Under development to meet this need are polymers that are improved in dynamic properties that have direct influences on the fuel efficiency of automobiles, like low rolling resistance and high wet traction.
Styrene-butadiene rubber (hereinafter referred to as “SBR”) or butadiene rubber (hereinafter referred to as “BR”), both known for use in tire treads for automobiles, may be prepared by two basically different processes: from solution (SSBR, solution styrene-butadiene rubber) or as an emulsion (ESBR, emulsion styrene-butadiene rubber). The first process, SSBR, is characterized by the polymerization of butadiene and styrene in a hydrocarbon solvent with an organolithium catalyst while the other approach (ESBR) is of emulsion polymerization initiated by a free radical, followed by the coagulation of the resultant latex into solid rubber. The SSBR process enjoys the advantage of controlling, as needed to arbitrary extent, micromolecular structures such as the vinyl unit of conjugated dienes, and styrene block contents, etc., as well as coupling rates and coupling numbers, which may account predominantly for physical properties of the polymer. Further, the SSBR process is advantageous over the ESBR process in that products prepared by the SSBR process are far superior in terms of rolling resistance and wet traction to those prepared by the ESBR process. Thanks to these advantages, the SSBR is widely used for the production of polymers which meet requirements for environment-friendly and high-performance tires.
Besides the dynamic properties, a methodological advantage is observed in the SSBR process. For example, a functional group introduced as a terminal modifier allows for the control of cold flow at ordinary temperatures as well as enabling a reinforcing material, when mixed, to improve in processibility and binding force, with consequent advance in dispersability. Particularly, a terminal modifier is configured to be compatible with carbon black and silica, usually used as reinforcing materials in tires, thereby making great contribution to improvement in wear resistance (tread wear) and rolling resistance in addition to wet traction.
There are many patents about SSBR processes that are configured to enhance the wet traction and rolling resistance of polymers by terminal modification.
U.S. Pat. No. 5,508,333 discloses a diene polymer which is modified at the terminus with an alkoxysilane containing an epoxy group and which has excellent dynamic and mechanical properties over conventional rubber. When applied to the terminus of the polymer, this terminal modifier forms a hydroxyl group. However, the terminal modifier, although modifying the terminus well, makes it impossible to control the extent of interpolymer coupling, which leads to a problem in controlling physical properties through coupling rate. In addition, this patent employs the reinforcing material carbon black, which causes environmental pollution, and the terminal modifier is only slightly miscible with silica, an environment-friendly reinforcement.
U.S. Patent Application Publication No. 20110207879 introduces a method characterized by the use of a diphenylethylene compound as a polymerization initiator so as to increase compatibility with carbon black and decrease rolling resistance. Since the diphenylethylene compound is not friendly to the environment, it is inappropriate for use in rubber for silica tires. Further, the initiator is inefficient in the polymerization of conjugate dienes, and is thus not economically beneficial, compared to general organolithium initiators.
U.S. Patent Application Publication No. 20100152369 describes the use of an alkoxysilane compound having a hydrolysable protecting group-substituted primary amine as a terminal modifier in the production of a conjugated diene polymer. For use in tire treads, a composition comprising the polymer modified with the terminal modifier, and silica can improve hysteresis loss, thus the physical properties of the tires. However, this method is poor in economy due to additional processes for the introduction and elimination of the protecting group, and the coupling rate is difficult to control with the method. In addition, cold flow, an important factor for storage stability, is measured to be high in the polymers, so that their shelf life is poor. Moreover, they still remain unsatisfactory for hysteresis and rolling resistance.
There is therefore an imperative need for novel, multifunctional conjugated diene polymers that overcome problems with conventional conjugated diene polymers, and that enhance mechanical and dynamic properties of rubber through an increase in compatibility with and dispersability of carbon black or silica, usual reinforcing agents in tires.